Not all TAFs are created equal

TAF meteorologists at the Charleston, SC WFO

Unless you have insider information you’d never know that there has been a subtle change to some terminal forecasts (TAFs) during the last few years. No, the coded TAF format hasn’t changed again as it did on November 5, 2008 when the world switched over to a revised TAF format that supports a 30 hour forecast. In fact, the TAFs don't look a bit different. But, for some high-impact airports in the U.S., TAFs are now issued more frequently. As all pilots are trained, TAFs are issued by the National Weather Service every six hours at the traditional synoptic times of 0000, 0600, 1200 and 1800 UTC. They generally get issued 20 to 40 minutes prior to these synoptic times. For the Chicago, Atlanta and New York City terminal areas TAFs are now issued every two or three hours. The NWS began this about five years ago as part of an enhanced aviation project for the FAA...and it went over so well that they adopted it permanently. For Chicago O'Hare Airport (KORD), you might even see 2-hourly updates at certain times during the day. The 2-hourly issuance times match the times of the FAA planning conference calls. Here’s the ugly side of this improvement. The 2- or 3-hourly forecast is treated as an amended forecast, not a newly constructed TAF. In fact, these non-standard scheduled TAFs will carry the AMD tag when viewed online or via a standard briefing. So there’s no way to tell if the forecast was changed because amendment criteria was reached or because it was time for a new forecast. Moreover, you won’t see a new forecast if an amendment has been issued within 90 minutes prior to the next 2- or 3-hour non-standard scheduled forecast. For many pilots, this subtle change won’t cause any significant impact to your current flight planning regiment. If you happen to fly into or out of a busy airspace such as Chicago, Atlanta or New York, just keep in mind that forecasts will be updated much more frequently even on those not so challenging weather days. In the end, if you see a terminal forecast tagged with AMD, it may not be because the previous forecast was misaligned with reality. It simply may be a new and improved forecast for you to ponder. Most pilots are weatherwise, but some are otherwise ™ Scott Dennstaedt Weather Systems Engineer CFI & former NWS meteorologist